Electronic reactance circuits



June 17, 1947. J, PLEBANsKl 2,422,257

ELECTRONIC REACTANCE C IRCUITS Filed June 20, l3.940

ATTORNEY Patented June 17, 1947 UNITED STATES PATENT OFFICE 2,422,257 l ELECTRONIC REACTANCE CIRCUITS New York Application June 20, 1940, Serial No. 341,487 In Poland April 26, 1935 9 Claims.

The present application is a continuation in part of my application Serial No. 73,865, led April l1, 1936, Patent No. 2,216,829, issued October 8, 1940. I

The present invention relates to electronic re- .actance circuits comprising an electron discharge tube arranged to act as an effective reactance; that is, either las a capacity or inductance, the value of which is controlled purely electrically by adjusting the amplification or internal impedance of the tube such as by controlling the bias potential appliedV to a grid or other control electrode. y

More particularly the invention is concerned with variable reactance tube circuits of the type wherein amplied output potential is fed back from the output circuit to the input circuit of the tube in quadrature phase relation to the current in the input circuit to produce a wattless reaction being the equivalent of a variation ofthe apparent reactance of the circuit.

Variable reactance tubes of the above type have various uses in practice, particularly for controlling the resonant frequency of a tuned circuit purely electrically without mechanically moving parts such as in automatic tuning systems for radio receivers or for phase and frequency modulation purposes and other applications.

An object of the invention is to provide an electronic reactance circuit which is both simple in design and eicient in operation compared. with circuits known in the prior art.

Another object is to provide an electronic reactance circuit which may be easily associated with a discharge tube already present in a circuit for other purposes such as the oscillator tube in a superheterodyne receiver.

These and further objects and advantages of the invention will become more apparent from the following detailed description taken with reference to the accompanying drawing forming part of this specication and wherein;

Figure 1 is a circuit diagram for a tuned amplifying stage embodying a wattless reaction or feedback circuit according to the invention for controlling the tuning or frequency response of the stage,

Figure 2 is a vector diagram explanatory of the function of the circuit according to Figure 1,

Figure 3 is a modification of the circuit arrangement according to Figure 1,

Figure 4 is a circuit diagram showing the circuit according rto the invention incorporated in a superheterodyne receiver to produce an automatic tuning or frequency control.

Like reference characters identify like parts in the different diagrams of the drawing.

Referring to Figure l, item I0 represents a source of alternating current such as high frequency signals arranged toexcite a resonant circuit comprised of an inductance coil I2 having in series therewith a resistance I4 and being shunted by .a tuning condenser I3. litem II is a coupling coil for impressing the signal currents from the source I0 upon the resonant circuit. In the example shown the resonant circuit forms the input coupling for an electron discharge tube I5l of any known type comprising in the example shown a cathode I6, an input control grid I1, a positively lbiased screen grid 25 and an anode or plate I8. The capacitative signal potential developed across the condenser I3 is impressed upon the grid-cathode path of the tube I5 resulting in corresponding amplied current variations in the anode or output circuit of the tube. The latter includes a tuned circuit comprised of an inductance 20 shunted by a condenser 22. The inductance 2l) is coupled with a further inductance 2I connected to a further amplifier or a utilization circuit by way of output terminals c-d. Item I9 is a known grid biasing network comprising a resistance tay-passed by a condenser and connected between the cathode and ground 24 or any other zero potential point of the system.

Thus far the circuit described constitutes a tuned R, F. amplier stage well known to those skilled in the art. In accordance with the present invention a portion of the amplified output energy is fed back in quadrature relation to the energy in the input or tuned circuit I2-I3-III by the provision of a regenerative or feedback path connected across the anode and cathode or ground and comprising a condenser 23 serving as a blocking condenser and the resistance I4 in series with the input circuit.

The function of Wattless or reactive feedback obtained in a circuit above described will be explained in the following: Starting with the oscillatory or circulatory current I'flowing in the resonant circuit I2-I3-I4 whose tuning adjustment is to be controlled, the capacitative poten' tial developed Iacross the condenser I3 and impressed upon the grid-cathode path of the tulbe I5 will lag the current I by an angle of 90 well understood by those familiar with the theo-ry of alternating current circuits. As a result thereof the potential developed on the plate I8 will lead the current I by the same angle due tothe phase reversal by the tube; that is, by Providing the condenser 23 has a sufficiently high capacity ance I2 and leading the current I by 90.

` and the resistance I4 has a sufficiently high value,

it is seen that the feedback current through the circuit 23-I4 will Ibe in phase with the potential at the plate I8; that is, it will lead the current I internal impedance of the tube I5. rI-he latter may be controlled in any known manner such as by means o-f an adjustable grid bias supplied by way of terminals a-b and controlled either manually or automatically as will be understood.

If the resistance I4 has a comparatively vsmall Value an exact reactive feedback is still obtainwill be understood by reference to Figure 2. In the latter the vVectorEiz represents the'inductive voltage drop developed across the tuning induit- T e voltage-drop E14 developed across the resistance I4 is in lphase with the-current I, thus yielding a resultant vector E12,14 equal to and of opposite phase tothe potential drop E13 developed across the'condenser I3 and impressed uponthe gridcathode path-of thetube -I 5. The voltage between the plate I8 andcathode Aisin turn opposite to the potential E1s -due ltothe phase reversal effected by the tube andhas a magnitude determined by the kamplification :constants or transcon'ductance of the tube. This holds true exactly if the output circuit 2li-'22 is in 'tune with the signal frequency vand laccordingly constitutes substantially an vohmicimpeda'nce so as not to introduce any additional phase shift of the output current. Since the sum of the potential drops developed by the condenser 23 and the resistance I4 forming theifeedback pathboth beingat quadrature must be'equal tolthe anode voltage'Eis it is seen that by proper design of the condenser 23 and the resistance I4 the 'respective potential drops E23 and E14 will be such that the latter constituting the effective regenerating or feedback potential impressed upon the input vcircuit leads the current I by exactly 90, thereby Iproducing the full effect of an apparent inductance increase of the circuit.

In Figure 3 there is shown a modified arrangei ment differing vfrom Figure 1 in that the entire ou-tput current is vpassed through the feedback resistance I4, the latter being connected in series withfthe tuning condenser 13. Afu'rther'blocking condenser I3 'is provided to prevent short circuit of the` anode to ground.

-Figure -4 shows "a circuit diagram for a superheterodyne receiver comprising an electron mixer tube of the pentagridor similar type for changing the incoming signals, of comparatively high frequency to intermediate'signals of lower frequency in a manner well known'and-serving simultaneously as an electronic reactance for automatically tuning the receiver vwithin a predetermined operating range to the frequency of an incoming signal.

Radio frequencysignals which may be derived from a preceding radio frequency amplifier or 'directly from an antenna are impressed by Way of input terminals a-b and coupling transformer primary 25 upon a tuned circuit comprising an inductance 26 in series with a blocking condenser 28 shunted by atuning `condenser 271. The tuned circuit 26-2 7 28 has its high potential side connected to thesignal input .grid 33 of an electron able by the proper size of the condenser 23 as 4 mixer 1tube 29 while the low Apotential side of the circuit is connected to ground 24 or any other zero reference point of the system. The D. C. return of the grid 33 may be effected in any known manner such as through an AVC circuit indicated in the diagram. The mixer tube as shown is of the pentagrid type and comprises a cathode 30, a first oscillating control grid 3 I, a positive or anode grid 32, an input signal grid 33 shielded by a "screen grid 34 andan anode or plate 35. Item 36 is a grid biasing network connected between the Acathode and ground comprising a resistance bypassed "bya condenser to provide proper biasing potential according to well known practice. Grids 3| and 32 are connected to a regenerative .circuit system for producing local oscillations -to be combined or mixed with the incoming signals so as to produce an intermediate frequency signal in the output circuit of the tube. The local oscillator, comprises a tank circuit formed by an inductance 311 havingin series therewith Va resistance 39 and shun-ted by a tuning condenser. The 1highpotentialside of this tank-circuit is connected'to the oscillating control grid 3l through a coupling condenser 42 while the lowpotential 'sideof the c'ircuit is grounded. The positive'or anode grid '-32 is connectedthrough:afeedback coil 40 arranged in inductive Arelation with the'oscillating inductance 31 tothe positive pole-of a suitable highfp'otential source indicated 5'bythe plus sign "and `bypassed to ground by a condenser 4I. The anode grid 32 is further connected tothe junction between the oscillating inductance 3'I and theres'istance 39 through feedbackcondenser 43 in a m'anner similar to that-described in 'connection with Figure 1.

The signals of intermediate `frequency produced by combining the local oscillation with the incorn-V ing signals are transmitted by means of an output circuit tuned to the lintermediate frequency comprising an inductance 45 shunted by a condenser 46 Aand connected betweenthe plate 35 and a suitable high .potential source indicated by the plus sign, :the latter ,being by-passed to ground through a condenser 41. The intermediatefrequency signals are applied by way of secondary winding 48 in inductive relation rwith the inductance 45 to an intermediate frequency amplier indicated by the rectangle 49. A detector and audio amplifier v5I) feeding a loudspeaker or the like 5I is connected tothe intermediateffrequency amplifier in a mannerwell known. Item 52 represents a discriminator or frequency response circuit associated with the 4interr'n'ediat'e frequency which Imay be of any known type and serves to produce 'a potential varying in proportion to deviations of the intermediate signal frequency 4from the xed intermediate 'frequencyfo'f `the system. v

Thisv frequency responsive (AFC) potential is impressed uponthe oscillating 'control grid `3I through a series resistanc'er5'4 and by-pass condenser 53 toconltrol theamounto'f oscillating current conveyed to the oscillating or anode grid 372 and in turn the `quadrature or wattless 'feedbacl current impressed upon the tank circuitv '3l- 384e 39 through :the feedback condenser '43;' i. 'e.,r`in turn the effective tuning adjustment of the circuit 31L-38'3'9.

Thus, whenever the "intermediate ffrequencyfd'- viates yfrom the desired value due to a Variation or drift of the signal frequency impressed by Away of terminals d b, a .positive or negative tune responsive potential Ais Vproduced l'by4 the `disc'rimi nator 52 resulting in a corresponding variationof the wattless-lf-ee'dback current 'and--in-tun "of the apparent reactance of the tank circuit both in sign and magnitude and within a predetermined range of frequency deviations. By proper adjustment of the polarity of discriminating potential, the detuning of the receiver will be automatically reduced to a minimum by the automatic frequency control of the local oscillator in the manner described. Contrary to the known automatic frequency control systems no special reactance or control tube is required when using a circuit as proposed by the present invention in addition to the other advantages and simplifications of both the design and operation of the system.

From the foregoing it will be evident that the invention is not limited to the specific circuits and arrangements of parts shown and disclosed therein for illustration, but that the principle of the invention will be susceptible of variations and modications coming within the broader scope of the invention as deiined in the appended claims. The specification and drawing are to be regarded accordingly in an illustrative rather than in a limiting sense.

I claim:

1. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control electrode, a tuned circuit carrying high frequency current coupled to said cathode and control electrode, a non-reactive impedance serially inserted in said tuned circuit, an output circuit connected to said anode, and a feedback circuit path between said anode and cathode including said non-reactive impedance, and means for controlling the degree of amplication of said tube.

2. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control electrode, a tuned input circuit carrying high frequency current comprising a capacitative and an inductive reactance in parallel, said tuned circuit being coupled to said control electrode `and cathode, a non-reactive impedance in series with one of said reactances of said tuned circuit, an output circuit connected to said anode, and a feedback circuit path between said anode and cathode including said non-reactive impedance.

3. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control grid, an input circuit carrying high frequency current comprising a condenser shunted by an inductance, said input circuit being coupled to said grid and .cathode, an ohmic resistance in series with said inductance, an output circuit connected to said anode, and a feedback circuit path between said anode and cathode including said ohmic resistance.

4. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control electrode, a tuned input circuit carrying high frequency current comprising an inductance `and a condenser in parallel, said tuned circuit being coupled to said control electrode and cathode, an ohmic resistance serially inserted in said tuned circuit, a further tuned circuit, and an output circuit connected to said anode, said further tuned circuit and said resistance being serially inserted in said output circuit.

5. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control grid, a tuned input circuit carrying high frequency current comprising an inductance shunted by a condenser, said input circuit being coupled to said grid and cathode, `an ohmic resistance in series with said inductance, a substantially non-reactive output circuit coupled to said anode and cathode, and a capacitative circuit connection between said anode and the junction point between said inductance and said resistance.

6. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode and at least one control grid, a, tuned input circuit carrying high frequency current comprising an inductance shunted by a condenser, said input circuit being coupled to said grid and cathode, an ohmic resistance in series With said inductance, a further tuned circuit coupled to said anode and cathode, and a capacitative circuit connection between said anode and the junction between said inductance and resistance.

7. An electronic reactance circuit comprising an electron discharge tube having a cathode, an anode andy at least one control grid, a, tuned input circuit carrying high frequency currents comprising an inductance shunted by a condenser, said input circuit being coupled to said grid and cathode, an ohmic resistance serially inserted in said input circuit, a further tuned circuit, and an output circuit coupled to said anode and cathode, said further tuned circuit and said resistance being serially inserted in said output circuit,

8. An electronic reactance circuit comprising a space discharge tube provided With a cathode, an anode, and at least one control grid, a circuit traversed by alternating current including reactive and non-reactive impedance in series, means for impressing reactive voltage drop from said lcircuit upon said grid and cathode, and a feedbacl circuit path between said anode and cathode including said non-reactive impedance.

9. An electronic reactance circuit compris-ing a space discharge tube provided With a cathode, an anode, and at least one control grid, a circuit traversed by alternating current including reactive :and non-reactive impedance in series, means for impressing reactive voltage drop from said circuit upon said grid and cathode, a feedback circuit path between said anode and cathode including said non-reactive impedance, and means for controlling the degree of amplification of said tube.

JOZEF PLEBANSKI.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,374,265 Baker etal Apr. 24, 1945 2,294,100 Travis Aug. 25, 1942 2,240,428 Travis Apr. 29, 1941 2,237,514 White Apr. 8, 1941 2,357,984 Travis Sept. 12, 1944 2,155,208 Travis Apr. 18, 1939 2,323,630 Spencer July 6, 1943 

